As described in a variety of patents, including U.S. Pat. Nos. 5,560,855, 5,156,653, 5,737,871, and 5,252,106, the teachings of each of which are incorporated herein by reference, it is desirable to tag organic liquids, particularly petroleum fuels, so that the tagged petroleum fuel may be identified for a variety of reasons, including tax purposes, e.g., road fuel vs. agriculture fuel, product brand identification, and quality, e.g., octane, identification. In many cases, particularly brand identification, the marker should be identifiable quantitatively to ensure against dilution of a tagged fuel with non-tagged fuel.
In a common tagging system, a marker is used which is soluble in fuel and is either not observable to the eye at the concentrations used or is used in conjunction with a dye which masks any color the marker may have. While the marker is soluble in petroleum fuel, it typically has a salt form that is soluble in either acidic or alkaline aqueous solution, whereby the marker may be extracted from the water-immiscible fluid by acidic aqueous solution or alkaline aqueous solution as the case may be. Because the marker is present in the fuel at low concentrations, typically between about 1 and about 100 ppm (parts per million by weight), it is usually a requirement that the marker, as extracted or subsequent thereto, undergo a chromophoric reaction, whereby presence of the marker is readily observable by its strong color.
While a relatively wide variety of such markers have been proposed, in actuality, only a relatively few have actually been accepted for use. There remains a need for additional markers to tag petroleum fuels and the like.
The use of chemicals as markers is to be distinguished from the use of chemicals as dyes. Dyes are used in petroleum fuels to impart color to the fuel. Dyes need only be soluble in petroleum fuel at a concentration so as to impart a desired color. They need not be extractable or color-forming, as is generally the case with markers.
The present invention is directed to a class of chemicals, some of which have been used as petroleum fuel dyes. These dyes, species of which are described in U.S. Pat. No. 5,142,030, the teachings of which are incorporated herein by reference, are not easily extracted. However, it is found herein that alkaline aqueous solutions employing particular co-solvents may be used to quantitatively extract such chemicals from organic fluids, including petroleum fuels.